1. Field of the Invention
The present invention provides an apparatus for making resin dental plates of full or partial dentures and a dental plate-making flask, which is used for carrying out said method.
2. Description of the Prior Art
Flasks used to prepare resin dental plates making use of the irradiation of microwaves involve a flask formed of fiber-reinforced synthetic plastic (hereinafter FRP for short) (Japanese Patent Application Laid-Open No. 61-263447) which is preferably used for carrying out a method for making dental plates using a thermally polymerizable resin as a dental plate (Japanese Patent Application Laid-Open No. 61-76149) and an FRP flask for a gypsum mold or a flask (Japanese Patent Application Laid-Open No. 63-220861) formed of a metal material such as stainless steel and/or a ceramic material which is proposed in view of a strength problem with such a FRP flask. Usually, a flask formed of such materials is provided at the center of its upper or lower lid with a sprue opening, as disclosed in Japanese Utility Model publication No. 61-10655, through which a pasted resin is cast into a gap or gaps for a dental plate formed of gypsum placed therein.
The strength problem with the above FRP flask is that a position of the sprue opening, through which a pasted resin is injected into the gap in the dental plate formed of gypsum placed in the flask, is located at the center of the upper or lower lid of the flask. In order to allow the pasted resin to prevail throughout the dental plate gap, it is essentially required to increase the length of the sprue to satisfy the need of providing various branchings of a passage through which the pasted resin flows. Consequently, a pressure under which the pasted resin is to be filled has to be increased, resulting in increased load so that this may pose a safety problem to the FRP flask. This is the reason why the FRP flask cannot be used as a resin injection type of flask. In view of this, it has been proposed to use a flask formed of a metal or ceramic material. A problem with a flask formed of a metal material is, however, that microwaves are reflected off the metal, producing an undesirable influence upon the process involved (e.g., unpolymerized matter being left as such). A problem with a flask formed of a ceramic material is, on the other hand, that it may not only crack or break, when it is dropped or receives an impact, but is also expensive.